This invention relates to adjusting mechanisms for automatically maintaining a uniform release clearance (and therefore a uniform stroke) for brakes and similar equipment. Mechanisms of this type are commonly used in brake systems to compensate for wear of the brake linings and other brake parts and are popularly called "automatic brake adjusters". Although the present invention is explained here in connection with brakes, the mechanism has utility in other environments where similar wear compensation is needed such as in clutches.
The basis adjuster designs have included mechanical adjusters with special ratchets or friction dragging parts to provide the adjustment for wear. Hydraulic adjusters utilizing the metering of hydraulic fluid and adjusters with deformable tubes have also been used.
The adjusters in which an enlarged deforming member is pulled through a ductile deformable tube have the advantage or low cost and reliability. Problems with this type of adjuster have included providing the tube with a sufficient wall thickness to carry compressive or tensile loads while at the same time reducing the wall thickness to a minimum so that it can be used on brakes where the adjusting force is low. The interdependency of the predetermined yield strength of the tube and the required tensile or compressive yield strength has limited the use of this type of adjusters to applications where the adjusting force is high. There has also been a problem in providing different adjustment load levels with the same adjuster because this has necessitated changing dimensions of the tube such as the wall thickness and diameter or it has required a different tube material.
Further problems encountered with adjusters of the type aforementioned have included a nonuniform resistance to deformation of the tube over its entire length. Tubing stressed in the manner previously described tends to deform more easily at its longitudinal end portions as opposed to its more central portions.